Conventionally, an evaporated fuel process system collects fuel vapor in a fuel tank and supplies the collected fuel vapor to an air intake system of an internal combustion engine. The evaporated fuel process system is equipped with a fuel vapor leakage detection device for detecting fuel vapor leakage of a fuel tank and a canister while the internal combustion engine is stopped. The fuel vapor leakage detection device includes, together with other components, a pump that pressurizes/de-pressurizes an inside of a fuel tank and a canister, a purge pipe that sends a fuel vapor that is adsorbed by the canister to the air intake system of the engine, and a purge valve that is disposed on the purge pipe for establishing a communication between an inside of the purge pipe to the air intake system, or for interrupting such communication therebetween. The disclosure of a patent document 1 (i.e., Japanese Patent Laid-Open No. 2002-202008) is in regards to a fuel vapor leakage detection device that compares a first electric current value and a second electric current value. The first electric current value is supplied to the pump for pressurizing an inside of the purge pipe when the purge valve is in a closed state. The second electric current value is supplied to the pump when the inside of the pressurized purge pipe is temporarily in communication with the air intake system, in order to detect a leakage and/or clogging of the purge pipe.
However, the fuel vapor leakage detection device in the patent document 1 cannot detect a clogging of an air passage that introduces air (i.e., atmosphere) into the canister. Therefore, when the air passage is clogged, fuel vapor that is adsorbed by the canister cannot be supplied to the air intake system.